/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 *
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

/*
 * Copyright 2019-2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package org.opensearch.performanceanalyzer.rca.framework.api.aggregators;

/**
 * To calculate the sliding window moving average.
 *
 * <p>So for a window size of 3: [1] : 1 [1, 10] : (1 + 10) / 2 [1, 10, 23] : (1 + 10 + 23) / 3 [1,
 * 10, 23, 33] : (10 + 23 + 33) / 3
 */
public class MovingAverage {
    private double sum;
    private int oldestElementIndex;
    private double[] lastNElements;
    private boolean isArrayFull;

    public MovingAverage(int window_length) {
        this.lastNElements = new double[window_length];
        this.oldestElementIndex = 0;
        this.sum = 0;
        this.isArrayFull = false;
    }

    /**
     * Takes the next input to the Average calculator.
     *
     * @param val Next value in the stream.
     * @return The average so far.
     */
    public double next(double val) {
        sum -= lastNElements[oldestElementIndex];
        sum += val;
        lastNElements[oldestElementIndex] = val;
        oldestElementIndex = (oldestElementIndex + 1) % lastNElements.length;
        if (!isArrayFull && oldestElementIndex == 0) {
            isArrayFull = true;
        }
        int count = lastNElements.length;
        if (!isArrayFull) {
            count = oldestElementIndex;
            return -1.0;
        }
        return (sum * 1.0f / count);
    }
}
